diff --git a/lib/index.js b/lib/index.js
index 36b3564..a7f568e 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -10,10 +10,6 @@ var many = require('./many.json')
 module.exports = normalize
 
 var own = {}.hasOwnProperty
-var assign = Object.assign
-
-var parse = bcp47.parse
-var stringify = bcp47.stringify
 
 var collator = new Intl.Collator()
 
@@ -27,75 +23,63 @@ var emptyExtraFields = {
 
 function normalize(value, options) {
   var settings = options || {}
-  var forgiving = settings.forgiving
-  var warning = settings.warning
   // 1. normalize and lowercase the tag (`sgn-be-fr` -> `sfb`).
-  var schema = parse(String(value || '').toLowerCase(), {
-    forgiving: forgiving,
-    warning: warning
-  })
-  var tag = stringify(schema)
-  var coreTag
-  // 2. Do fancy, expensive replaces (`ha-latn-gh` -> `ha-gh`).
-  var length = matches.length
+  var schema = bcp47.parse(String(value || '').toLowerCase(), settings)
+  var tag = bcp47.stringify(schema)
   var index = -1
-  var d
+  var key
 
-  if (tag === '') {
+  if (!tag) {
     return tag
   }
 
-  while (++index < length) {
-    d = matches[index]
-    if (match.extendedFilter(tag, d.from).length > 0) {
-      replace(schema, d.from, d.to)
-      tag = stringify(schema)
+  // 2. Do fancy, expensive replaces (`ha-latn-gh` -> `ha-gh`).
+  while (++index < matches.length) {
+    if (match.extendedFilter(tag, matches[index].from).length) {
+      replace(schema, matches[index].from, matches[index].to)
+      tag = bcp47.stringify(schema)
     }
   }
 
   // 3. Do basic field replaces (`en-840` -> `en-us`).
-  length = fields.length
   index = -1
 
-  while (++index < length) {
-    d = fields[index]
-
-    if (remove(schema, d.from.field, d.from.value)) {
-      add(schema, d.to.field, d.to.value)
+  while (++index < fields.length) {
+    if (remove(schema, fields[index].from.field, fields[index].from.value)) {
+      add(schema, fields[index].to.field, fields[index].to.value)
     }
   }
 
   // 4. Remove defaults (`nl-nl` -> `nl`).
-  coreTag = stringify(assign({}, schema, emptyExtraFields))
-  length = defaults.length
+  tag = bcp47.stringify(Object.assign({}, schema, emptyExtraFields))
   index = -1
 
-  while (++index < length) {
-    d = defaults[index]
-
-    if (coreTag === d) {
-      replace(schema, d, d.split('-').slice(0, -1).join('-'))
-      coreTag = stringify(assign({}, schema, emptyExtraFields))
+  while (++index < defaults.length) {
+    if (tag === defaults[index]) {
+      replace(
+        schema,
+        defaults[index],
+        defaults[index].split('-').slice(0, -1).join('-')
+      )
+      tag = bcp47.stringify(Object.assign({}, schema, emptyExtraFields))
     }
   }
 
-  tag = stringify(schema)
-
   // 5. Sort extensions on singleton.
   schema.extensions.sort(compareSingleton)
 
   // 6. Warn if fields (currently only regions) should be updated but have
   // multiple choices.
-  if (warning) {
-    for (d in many) {
-      if (own.call(many[d], schema[d])) {
-        warning(
+  if (settings.warning) {
+    for (key in many) {
+      if (own.call(many[key], schema[key])) {
+        settings.warning(
           'Deprecated ' +
-            d +
+            key +
             ' `' +
-            schema[d] +
+            schema[key] +
             '`, expected one of `' +
-            many[d][schema[d]].join('`, `') +
+            many[key][schema[key]].join('`, `') +
             '`',
           null,
           7
@@ -106,29 +90,29 @@ function normalize(value, options) {
 
   // 7. Add proper casing back.
   // Format script (ISO 15924) as titlecase (example: `Latn`):
-  if (schema.script !== null) {
+  if (schema.script) {
     schema.script =
       schema.script.charAt(0).toUpperCase() + schema.script.slice(1)
   }
 
   // Format region (ISO 3166) as uppercase (note: this doesn’t affect numeric
   // codes, which is fine):
-  if (schema.region !== null) {
+  if (schema.region) {
     schema.region = schema.region.toUpperCase()
   }
 
-  return stringify(schema)
+  return bcp47.stringify(schema)
 }
 
 function replace(schema, from, to) {
-  var left = parse(from)
-  var right = parse(to)
+  var left = bcp47.parse(from)
+  var right = bcp47.parse(to)
   var removed = []
   var key
 
   // Remove values from `from`:
   for (key in left) {
-    if (defined(left[key]) && remove(schema, key, left[key])) {
+    if (left[key] && left[key].length && remove(schema, key, left[key])) {
       removed.push(key)
     }
   }
@@ -138,8 +122,9 @@ function replace(schema, from, to) {
     // Only add values that are defined on `to`, and that were either removed by
     // `from` or are currently empty.
     if (
-      defined(right[key]) &&
-      (removed.indexOf(key) !== -1 || !defined(schema[key]))
+      right[key] &&
+      right[key].length &&
+      (removed.indexOf(key) > -1 || !schema[key] || !schema[key].length)
     ) {
       add(schema, key, right[key])
     }
@@ -150,7 +135,6 @@ function remove(object, key, value) {
   var removed = false
   var current
   var result
-  var length
   var index
   var item
 
@@ -161,15 +145,14 @@ function remove(object, key, value) {
     current = object[key]
     result = current
 
-    if (array(current)) {
+    if (current && typeof current === 'object') {
       result = []
-      length = current.length
       index = -1
 
-      while (++index < length) {
+      while (++index < current.length) {
         item = current[index]
 
-        if (value.indexOf(item) === -1) {
+        if (value.indexOf(item) < 0) {
           result.push(item)
         } else {
           removed = true
@@ -189,21 +172,19 @@ function remove(object, key, value) {
 function add(object, key, value) {
   var current = object[key]
   var list
-  var length
   var index
   var item
 
-  if (array(current)) {
+  if (current && typeof current === 'object') {
     list = [].concat(value)
-    length = list.length
     index = -1
 
-    while (++index < length) {
+    while (++index < list.length) {
       item = list[index]
 
       /* istanbul ignore else - this currently can’t happen, but guard for the
        * future. */
-      if (current.indexOf(item) === -1) {
+      if (current.indexOf(item) < 0) {
         current.push(item)
       }
     }
@@ -212,24 +193,6 @@ function add(object, key, value) {
   }
 }
 
-function defined(value) {
-  return value !== null && value.length !== 0
-}
-
-function array(value) {
-  return value !== null && typeof value === 'object'
-}
-
 function compareSingleton(left, right) {
-  return compare(singleton(left), singleton(right))
-}
-
-function compare(left, right) {
-  /* istanbul ignore next - equality can’t happen in BCP 47 tags, but let’s keep
-   * it in as a guard. */
-  return left === right ? 0 : collator.compare(left, right)
-}
-
-function singleton(value) {
-  return value.singleton
+  return collator.compare(left.singleton, right.singleton)
 }
diff --git a/package.json b/package.json
index 697cfff..6caa340 100644
--- a/package.json
+++ b/package.json
@@ -65,6 +65,7 @@
     "prettier": true,
     "esnext": false,
     "rules": {
+      "unicorn/explicit-length-check": "off",
       "unicorn/prefer-includes": "off",
       "unicorn/prefer-number-properties": "off",
       "unicorn/prefer-set-has": "off"